1. Field of the Invention
The present invention relates to a simple novel process for producing nanostructures, and particularly to a method of synthesizing carbon nanorods (CNRs) and nanowires (CNWs) through the use of cross-linked resorcinol-formaldehyde gel as a precursor.
2. Description of the Related Art
Since the discovery of the C60 buckminsterfullerene molecule, there has been much interest in the field of carbon nanorods (CNRs) and carbon nanowires (CNWs). The explosion in C60 research in the early 1990s was driven by the production of large quantities (which was in the order of few milligrams) of this material using a high pressure arc discharge method. A nanowire refers to a wire having a diameter typically in the range of about 1 nm to about 500 nm. Nanowires, such as small-sized CNTs (carbon nanotubes) on the order of 1-100 nm in diameter and 0.1-100 microns in length, have received considerable attention in recent years. Nanowires are solid structures, which can have an amorphous, graphite or a herringbone structure. Nanowires are periodic only along their axes, and therefore they can assume any energetically favorable order in other planes, resulting in a lack of crystalline order.
The dimensions of nanoparticles, located between those of molecules and conventional microelectronics, allow mimicking of nature's efficient ways of managing with less when it comes to chemical and physical processing. Nanorods can be used in various fields, such as catalysts, medicine and pharmaceuticals, electronic devices, nanoelectronics, nanophotonics, ceramic materials, pigments and cosmetics industry. The U.S. has invested more than $8 billion in nanotechnology research and development since the year 2000, and the National Science Foundation (NSF) estimates the global market for nanotechnology products will be about $1 trillion by 2015. In its 2007 strategic plan, the National Nanotechnology Initiative, which oversees U.S. nanotechnology research spending, pointed to the critical need for synthesis and processing techniques that yield high-quality, pure nanomaterials. The global markets of nanotechnology are vast in general and still virgin for nanorods and nanowires in particular.
So far, various methods have been demonstrated for the synthesis of CNRs and CNWs, which include the arc discharge method, chemical vapor deposition/template methods, electron beam-induced route, and catalytic copyrolysis method. One technique for fabricating nanowires utilizes a micro lithographic process followed by metal organic chemical vapor deposition (MOCVD). This technique may be used to generate a single quantum wire or a row of gallium arsenide (GaAs) quantum wires embedded within a bulk aluminum arsenide (AlAs) substrate. One problem with this technique, however, is that micro-lithographic processes and MOCVD have been limited to GaAs and related materials.
Moreover, this technique does not result in a high degree of size uniformity of the wires suitable for practical applications. Another method of fabricating nanowires involves using a porous substrate as a template and filling naturally occurring arrays of nano-channels or pores in the substrate with a material of interest. However, it is difficult to generate relatively long continuous wires having relatively small diameters because as the pore diameters become small, the pores tend to branch and merge. As a result, the small and long pores present difficulties in filling the tube with the desired filling material.
Unlike nanowires, CNTs are hexagonal networks of carbon atoms forming hollow, seamless tubes with each end capped with half of a fullerene molecule. They were first produced as multi-layer concentric tubes or multi-walled CNTs by evaporating carbon in an arc discharge. Presently, there are three main approaches for the synthesis of single and multi-walled CNTs. These include the electric arc discharge of graphite rod, the laser ablation of carbon, and the chemical vapor deposition of hydrocarbons. Unfortunately, these methods are not suitable for the production of nanowires, especially for commercial investment. Besides, CNRs or CNWs are obtained from the above methods as byproducts of CNTs, rather than as the primary product. As such, these methods are considered indirect methods for preparing CNRs or CNWs. Therefore, there is a dire need for a convenient and simple method for synthesizing CNRs and CNWs.
Thus, a method of synthesizing carbon nanorods and nanowires solving the aforementioned problems is desired.